Sea duck

A duck
(family
Anatidae) associated to a greater or lesser extent
with a marine rather than a freshwater
habitat.
Some of these
are called 'bay ducks' in North America. The Eider Somateria
mollissima is the only example occurring commonly in the British
Isles which is marine throughout the year, but a number of others,
such as the Scaup Aythya marila, the Long-tailed Duck Clangua
hyemalis and the scoters
(genus
Melanitta) spend the winter
mainly on the sea. The Shelduck Tadorna tadorna and the
Wigeon Anas penelope, although much associated with coasts,
are more characteristic of
estuary
or
saltmarsh
habitats than
the sea itself and so would not normally be called 'sea ducks'.